A panoramic photograph is a photograph with an unusually large field of view, an exaggerated aspect ratio, or both. For example, a horizontal panoramic photograph is much wider than its height, and has a horizontal angle of view that is large in relation to its vertical angle of view. A vertical panoramic photograph is much taller than its width, and has a vertical angle of view that is large in relation to its horizontal angle of view.
Historically, panoramic photographs have been taken using specially-made cameras. One kind of panoramic camera uses a rotating lens and body to sweep across a large field of view while moving film past a narrow exposure slit behind the lens. This kind of rotating camera, sometimes called a “Cirkut-type” camera after an early commercial model, can take a photograph with a field of view of 360 degrees or more. A swing-lens camera operates on a similar principle, but rotates its lens and the exposure slit in relation to a stationary body and film. A swing-lens camera can take a photograph with a field of view somewhat less than 180 degrees.
Another method of making a panoramic photograph is to take several overlapping conventional photographs, each typically having an aspect ratio of about 3:2, and then join them together into a single larger photograph. The joining is typically done using a computer operating on digital representations of the component photographs. The digital representations may be obtained by scanning photographic film or prints, or may be obtained directly using a digital camera to photograph the subject. This process of combining digital images into a larger photograph is often called stitching.
FIGS. 1A-1D illustrate the process of creating a panoramic photograph from component photographs. FIG. 1A shows a landscape scene 100 with a wide aspect ratio. FIG. 1B shows three overlapping component photographs 101, 102, 103 of a conventional aspect ratio, taken so that each portion of scene 100 that is to be included in the resulting panoramic photograph is represented in at least one of the component photographs 101-103. FIG. 1C shows component photographs 101-103 in isolation. Certain features such as tree 104 and fence corner 105 appear in more than one of the component photographs, and may be used by the stitching process to align component photographs 101-103 with each other. FIG. 1D shows a panoramic photograph 106 constructed by stitching component photographs 101-103 together. Methods are known in the art for accomplishing the stitching.
It is desirable that all of a set of component photographs be taken using the same exposure and focus settings. For example, if a film camera is used to take the component photographs, the camera would be set to use the same lens aperture and exposure time for all of the photographs. If the camera used to take the component photographs is a digital camera, additional settings may be held constant as well, including the system gain (or ISO setting), white balance, or other settings.
Some Cirkut-type cameras can scan the panoramic scene that is to be photographed and automatically select exposure settings appropriate for the entire scene. However, a conventional camera, which may be used to take a set of component photographs that will be later stitched into a panoramic photograph, has a limited field of view.
Some modern digital cameras provide a mode that assists a user of the camera in taking a set of component photographs for later stitching into a panoramic photograph. A panoramic mode may use a display screen on the camera to assist the user in framing each component photograph for proper overlap with previous photographs in the set, and may ensure consistent exposure settings for all of the component photographs in a set. For example, upon being put in a panoramic mode, the camera may automatically determine focus and exposure settings for the next photograph taken, and then use those same settings for each subsequent photograph taken until the panoramic mode is exited.
However, using exposure settings, focus settings, or both determined from only the first photograph in the sequence (often the leftmost component photograph of a horizontal panorama) can result in improper exposure or focus for the panorama if the portion of the scene metered for the first photograph is not representative of the entire scene. FIG. 1A provides an example of a scene likely to be improperly exposed. Setting sun 107 creates a bright portion of the scene, and is the main subject of interest. Exposure settings determined from the darker scene portion covered by component photograph 101 will likely result in an overexposed component photograph 102, ruining the resulting panorama 106. Similarly, a focus setting selected for component photograph 101 may not be appropriate for the entire scene. For example, the camera may choose tree 108, near the camera, in photograph 101 as a focus subject, with the result that distant objects, including sun 107 and most other objects in component photographs 102 and 103, are out of focus.